1. Field of the Invention
The present invention relates to a technique for printing images by recording dots on the surface of a printing medium by ejecting ink droplets from a plurality of nozzles, and more particularly to a printing technique that utilizes a nozzle test for testing whether or not ink droplets are ejected from each nozzle.
2. Description of the Related Art
Ink jet printers print images by ejecting ink droplets from a plurality of nozzles. Numerous nozzles are provided to the printing head of an ink jet printer, but there are instances when of some the nozzles become clogged and are unable to eject ink droplets due to an increase in the viscosity of the ink, the admixture of bubbles, or another such cause. In particular, if an ink jet printer is left for an extended period without printing anything, the viscosity of the ink can increase to the point that ink droplets can no longer be ejected from the nozzles. When a nozzle becomes clogged, dots will be missing in the image, which adversely affects image quality. In this Specification, a test of the nozzles is also referred to as a xe2x80x9cmissing dot test.xe2x80x9d
In order to clear the nozzles of clogging, a cleaning mechanism is ordinarily provided to an ink jet printer. The user can press a button on the printer and clean the nozzles whenever desired. Also, to deal with situations when the printer is left unused for extended periods as above, the printer itself is sometimes designed so that it automatically performs cleaning whenever a specific length of time has elapsed from a predetermined point in time.
However, although some measures in the cleaning sequence and in the construction of the cleaning mechanism are taken and vary rare, there are cases rarely in which a nozzle that had not been clogged before cleaning becomes clogged as a result of cleaning. In such a case, cleaning in an attempt to eliminate clogged nozzles can actually increase the likelihood of creating nozzle clogging.
Accordingly, an object of the present invention is to reduce the likelihood of generating nozzle clogging.
In order to attain at least part of the above and other objects, there is provided a printer comprising a printing head having a plurality of nozzles for ejecting ink droplets, a cleaning mechanism for cleaning the plurality of nozzles, and a test unit for testing whether each of the plurality of nozzles can eject ink droplets. When the cleaning mechanism performs cleaning for a specific inducement other than the detection by the test unit of at least a specific number of non-operating nozzles unable to eject ink droplets, automatically carrying out the testing of the nozzles by the test unit before and/or after this cleaning. The following description will be divided into two cases: when the testing is conducted before cleaning, and when the testing is conducted after cleaning.
(1) Test After Cleaning:
In one embodiment, when the cleaning mechanism performs cleaning for the specific inducement other than the detection by the test unit of non-operating nozzles unable to eject ink droplets, the testing of the nozzles can be automatically carried out by the test unit after this cleaning. This makes it possible to ascertain whether the nozzles are clogged when there is the possibility that nozzle clogging will not be cleared by cleaning. Therefore, the reduction in image quality can be ameliorated by choosing a suitable printing operation according to whether there is any clogging after cleaning.
When a non-operating nozzle is detected by the testing of the nozzles after cleaning, and a nozzle array to be used for printing can be made up of just operating nozzles, it is preferable for the printing to be carried out using a nozzle array made up of just operating nozzles. If this is done, then even if there are some non-operating nozzle, normal printing can still be carried out with just the operating nozzles.
When a non-operating nozzle is detected by a test of the nozzles after cleaning, and a nozzle array to be used for printing can be made up of not just operating nozzles but with the non-operating nozzle, it is preferable for the printing to be carried out according to a printing operation including a supplemental operation in which dots on a main scanning line to be recorded by the non-operating nozzle in the nozzle array are recorded using one of the operating nozzles. If this is done, the dots that are supposed to be recorded by the non-operating nozzle can be recorded by the other operating nozzles, thereby preventing a decrease in image quality.
The cleaning may include an operation in which ink is drawn out of the plurality of nozzles by suction. With cleaning such as this, there is believed to be a likelihood that some nozzles which were not clogged prior to cleaning will be clogged after cleaning, although some measures in the cleaning sequence and in the construction of the cleaning mechanism are taken. Therefore, the above-mentioned effect will be particularly great if a nozzle test is conducted after such cleaning. Furthermore, conducting a test of the nozzles after cleaning makes it possible to simplify the complex cleaning mechanism.
(2) Test Before Cleaning:
In one embodiment, when the cleaning mechanism performs cleaning for the specific inducement other than the detection by the test unit of at least a specific number of non-operating nozzles unable to eject ink droplets, the testing of the nozzles can be automatically carried out by the test unit before this cleaning.
This makes it possible to ascertain whether the nozzles are clogged before cleaning. There is also the possibility that nozzles which are not clogged will become clogged when cleaned. If the above procedure is followed, however, it can be ascertained whether the nozzles are clogged prior to cleaning, so a decision not to clean can be made according to the number of clogged nozzles, thereby lowering the potential for new clogging to occur.
The excluded inducement, xe2x80x9cthe detection of at least a specific number of non-operating nozzles,xe2x80x9d may be xe2x80x9cthe detection of one or more non-operating nozzles.xe2x80x9d The nozzle test may also be performed both before and after cleaning. Specifically, it can be performed before cleaning, after cleaning, or both.
It is preferable to cancel the cleaning if the number of non-operating nozzle detected by the testing of the nozzles before cleaning is less than a first threshold. Even in this case, however, flushing (blowing out the ink) may be performed. The phrase xe2x80x9cif the number of non-operating nozzle is less than a first thresholdxe2x80x9d as used here encompasses xe2x80x9cless than one,xe2x80x9d that is, xe2x80x9cif no non-operating nozzles are detected.xe2x80x9d
The above procedure more effectively lowers the probability that the cleaning of nozzles which are not clogged will result in new clogging and non-operating nozzles. Furthermore, if the amount of ink consumed in the cleaning of the nozzles is greater than the amount of ink consumed in the testing of the nozzles, ink consumption can be kept lower than when cleaning is carried out directly by choosing whether or not to execute the cleaning as above.
The cleaning for the specific inducement preferably includes timer cleaning carried out automatically by the printer when at least a specific amount of time has elapsed since a specified event.
If a printer of the type that ejects ink droplets from nozzles is left for an extended period without printing anything, the viscosity of the ink can increase to the point that ink droplets can no longer be ejected from the nozzles. If the nozzles are automatically cleaned after a specific length of time has elapsed since printing or nozzle cleaning as above, however, this blocked ejection caused by the thickening of the ink can be effectively prevented.
Furthermore, in the above embodiment, this automatic cleaning will not be performed if the number of non-operating nozzles detected by the nozzle test before cleaning is less than a first threshold, so the likelihood that non-operating nozzles will result from the cleaning itself can also be reduced.
Further, in the above embodiment, if it is decided not to clean, then another attempt at automatically cleaning the nozzles will be made when the specified length of time has elapsed from that decision. Thus, with the above embodiment, testing is carried out at regular time intervals after the last printing, and the nozzles are cleaned according to the number of clogged nozzles. Accordingly, the nozzles of the printer are always kept in good condition, and the printer remains ready to print right away even after not having been used for an extended period.
It is also preferable for the plurality of nozzles to be divided into a plurality of nozzle sets each including one or more nozzles, and for a decision to be made whether to cancel the execution of the cleaning for each nozzle set when the cleaning mechanism is able to carry out independently the cleaning for each of the nozzle sets. With this embodiment, cleaning is carried out for those nozzle sets including non-operating nozzles, but not for those nozzle sets that do not include any non-operating nozzles, allowing the cleaning to be performed more efficiently.
Meanwhile, it is preferable to require a user to reconfirm a cleaning directive if the execution of the cleaning for the specific inducement is a result of the cleaning directive from the user, and if the number of non-operating nozzles detected by the testing of the nozzles before the cleaning is less than a first threshold.
If this is done, the user can decide whether to perform cleaning on the basis of the number of non-operating nozzles. Specifically, the user chooses whether to clean the nozzles even though the number of non-operating nozzles is less than the specified number, or not to clean the nozzles. Therefore, with this embodiment, the likelihood that cleaning will result in new clogging can be reduced on the whole, while still respecting the will of the user.
Furthermore, when the user inputs a cleaning directive prior to printing text, graphics, or the like just to be on the safe side, the time this cleaning takes can be reduced and the printing carried out more quickly if the user opts not to perform the cleaning if the number of non-operating nozzles is less than the first threshold. As to the time it takes to test the nozzles, the longer it takes to clean the nozzles, the more time that can be saved by making the above selection.
The cleaning may include an operation in which ink is drawn out of the plurality of nozzles by suction. With cleaning such as this, the likelihood that nozzles which were not clogged prior to cleaning will be clogged after cleaning is relatively high, although some measures in the cleaning sequence and in the construction of the cleaning mechanism are taken. Therefore, if a nozzle test is conducted before this cleaning, the likelihood of clogging can be effectively reduced by selecting whether or not to execute the cleaning after this test.
It is also preferable that a plurality of sequences are prepared in advance for the cleaning, and to select one of the cleaning sequences according to the number of non-operating nozzles detected by the testing of the nozzles before the cleaning. With this embodiment, the appropriate cleaning sequence can be carried out as dictated by the number of non-operating nozzles.
It is also preferable to select a first cleaning sequence having a plurality of cleaning operations, including a first cleaning operation and a second cleaning operation, when the number of non-operating nozzles detected by the testing of the nozzles before the cleaning is less than a second threshold, and to select a second cleaning sequence including the cleaning operations beginning with the second cleaning operation out of the first cleaning sequence when the number of non-operating nozzles detected by the testing of the nozzles before the cleaning is at least the second threshold. The first cleaning operation here is a cleaning operation whose ability to clear nozzle clogging is relatively low and which is carried out relatively early in the cleaning sequence. The second cleaning operation is a cleaning operation whose ability to clear nozzle clogging is relatively high and which is carried out relatively late in the cleaning sequence.
With this embodiment, when the number of non-operating nozzles is large, the first cleaning operation with its relatively low ability to clear nozzle clogging is skipped and the second cleaning operation is carried out, allowing the cleaning to be performed more efficiently.
It is preferable for each of the plurality of cleaning operations in the first cleaning sequence to be carried out when the nozzle clogging has not been cleared by a previous cleaning operation. If this is done, nozzle clogging can be cleared efficiently, without wasting time on any unnecessary cleaning operations.
The following is preferable if the plurality of nozzle sets include a first nozzle group consisting of nozzles that eject ink with which nozzle clogging is relatively easy to clear, and a second nozzle group consisting of nozzles that eject ink with which nozzle clogging is relatively difficult to clear. Specifically, a first cleaning sequence is selected when all of the non-operating nozzles detected by the testing of the nozzles before the cleaning are included in the first nozzle group. On the other hand, a second cleaning sequence is executed when the non-operating nozzles detected by the testing of the nozzles before the cleaning include the nozzle of the second nozzle group. Details of the first cleaning sequence and second cleaning sequence are as given above.
With this embodiment, if there are nozzles that eject ink with which nozzle clogging is difficult to clear are among the non-operating nozzles, then the first cleaning operation with its relatively low ability to clear nozzle clogging is skipped and the second cleaning operation is carried out, allowing the cleaning to be performed more efficiently.
If the plurality of nozzles are divided into a plurality of nozzle sets each including one or more nozzles, and the cleaning mechanism is able to carry out each of the plurality of cleaning operations independently for each of the nozzle sets, it is preferable to determine the cleaning sequence carried out for each nozzle set. With this embodiment, appropriate cleaning can be carried out for easy nozzle set according to the extent of nozzle clogging.
The present invention can be realized through various embodiments such as those given below.
(1) A method for controlling a printer, and a printing method
(2) A printing controller, and a printer
(3) A computer program for realizing the above devices and methods
(4) A recording medium on which is recorded a computer program for realizing the above devices and methods
(5) A data signal embodied in a carrier wave and including a computer program for realizing the above devices and methods